GM Service Manual Online
For 1990-2009 cars only

If your vehicle has an Allison 1000/2000/2200/2400/2500 series automatic transmission, a lighted bar under the current gear selected will flash.

If your vehicle has an Allison 3000/3500 series automatic transmission, the current gear selected on the pushbutton display will flash.

The flashing bar or gear selection indicates that transmission range shifts may not occur.

For detailed information on shift inhibit limitations, see the Allison Automatic Transmission Operator's Manual in your vehicle for further information.